Testing apparatus



Jan. 18, E E' MRTENSSON TESTING APPARATUS Filed Jan. l0, 1935 Patented`ian. 18, 1938 UETED STA'EES ATENT OFFICE Application January 10, 1935,Serial No. 1,088 In Sweden September 15, 1934 4 Claims.

The present invention relates to an arrangement for generating directVoltage of high tension which is particularly adapted for use as asource of voltage in portable electrical testing apparatus, for instancefor testing the insulating resistance and for detecting insulatingfaults in condensers, cables or the like.

Arrangements are previously known by means of which direct voltage canbe obtained by charging one or more condensers from an alternatingcurrent source through valves serving as rectiers. Said knownarrangements are, however, expensive and complicated and are on accountof their considerable weight and of the great mechanical sensitivity ofthe rectier arrangement not suitable for use as a source of voltage inportable testing apparatus.

According to the present invention a very light, simple, and robustarrangement for generating direct voltage has been obtained bysubstituting for the valves a spark gap or other similar discharge pathand by selecting as the source of current -an induction coil of smalldimensions connected to a small battery, preferably a dry cell. In apreferred embodiment of the invention there is connected in parallelwith thecondenser to be charged a leakage circuit for controlling thevoltage of said condenser, which leakage circuit includes a glowdischarge lamp or other discharge path and, in some instances, also anohmic resistance. When using the arrangement according to the inventionas the source of current in portable electrical testing apparatus theglow discharge lamp included in the leakage circuit can preferably beused also as the current indicator during the tests, `the glow dischargelamp being included in the leakage circuit during the periodof chargingthe condenser and between the terminals of the condenser in-series withthe object to be tested during the testing period.

The invention will be more closely described with reference to theaccompanying drawing which shows an arrangement according to theinvention used as a source'oi test voltage in an electrical insulationtesting apparatus.

Referring to thedrawing, Il) indicates an induction coil the secondarywinding of which is connected to two wires i and I5 and the primarywinding of which is fed from a battery I3, the positive terminal I2 ofthe battery being connected to the make and break contact through wiresII, and the negative terminal IQ being adapted to be connected to theother end of the primary winding by means of a push button switch I5over the wire I5 and a wire 2. To the wire I is connected one terminalof the spark gap 3 the other terminal of which is connected by a wire ito one terminal of the condenser 6 to be charged. The other terminal ofthe condenser 6 is connected to the wire I5. To the rst 5 mentionedterminal of the condenser 6 is also connected one terminal of the glowdischarge lamp 'I the other terminal of which is adapted to be connectedto the second terminal of the condenser S to be charged, either througha series 10 resistance Il' and a switch I8 mechanically coupled with theswitch I6, or through a series resistance 8, a switch I9 and the objectto be tested 36 which is connected between the connecting terminals and2I. l5

Between the positive terminal I2 of the battery I3 and the connectingterminal 20 is included an incandescent lamp 22 in series with a pushbutton switch 23. 'I'he other connecting terminal 2I is permanentlyconnected over the wire I5 to the negative terminal I4 of the batteryI3.

There is indicated an extra arrangement for testing for instance thedielectric strength of cables. The wire I is by means of a wire 24connected to a connecting terminal 25. Between the wires I5 and 2li isincluded an adjustable spark gap 26. The cores of the cable betweenwhich the dielectric strength is to be tested are connected to theconnecting terminals 2| and 25 respectively.

The testing apparatus is used in the following manner:

It will be assumed that the insulation of a condenser 3B is to betested. After the condenser 35 has been included between the connectingterminals 20 and 2|, the push button IB, I8 is pressed. A feed circuitis then closed from the battery I3 to the induction coil IIJ via theswitch it, and the glow discharge lamp 'I is included in series with theseries resistance I'I in a circuit connected in parallel with thecondenser 6. The induction coil IQ is started whereafter the charging ofthe condenser 6 to the desired test voltage takes place in the followingmanner:

When upon the pressing of the button I6, I8 the voltage of the inductioncoil approaches its greatest maximum value (for instance its positivemaximum value) the voltage across the spark gap 3 will exceed theignition Voltage, an arcingover then taking place causing the condenserto receive a certain charge. The voltage of the condenser then risessomewhat. When thereafter the voltage of the induction coil dropsthrough zero to its negative maximum value the condenser will evidentlyget a tendency to discharge across the spark gap. The sum of thecondenser voltage and the negative maximum voltage of the inductionvcoilwill, however, not reach a value amounting to the ignition Voltage cfthe spark gap wherefore the charge received remains on the condenser.the induction coil approaches its positive maximum value the next time,an arcing-over will again occur in the spark gap, and the condenserreceives a further charge so that its Voltage is further increased. Inthis manner the condenser is charged in steps until its voltage hasreached a value corresponding to the ignition Voltage of the glowdischarge lamp 'I connected in parallel therewith. When this occurs aflashover will take place in the glow discharge lamp l so that a leakagecircuit including the glow discharge lamp l and its series resistance I7is closed across the condenser Ei. The leakage current through saidcircuit is to begin with very insignificant, because as long as thevoltage across the condenser is low the glow discharge lamp will take upthe greater part of the voltage drop. According as the voltage on thecondenser is increased the seriesr resistance will, however, take up agreater part of the total voltage drop wherefore the leakage currentincreases more rapidly than the voltage of the condenser 6 to becharged. On the other hand, the charge supplied to the condenser foreach period of the pulsating alternating voltage becomes smaller andsmaller the higher the condenser voltage gets. When the quantity ofelectricity charged into the condenser 6 per unit of time becomes equalto the quantity of electricity passing from the condenser through theleakage circuit in the same period of time a condition of equilibriumwill evidently exist upon the reaching of which the voltage does notrise any longer in spite of the button I6, I3 being kept continuouslypressed. By suitably dimensioning the series resistance I1, it isevidently possible to prevent the condenser voltage from reaching sohigh a value that the sum of said voltage and the negative maximumvoltage of the induction coil amounts to the ignition voltage of thespark gap. The discharge of the condenser 6 across the spark gap 3 ishereby effectively prevented. On the other hand, the final voltage ofthe condenser 6 must be considerably higher than the ignition voltage ofthe glow discharge lamp 1 since in the shown apparatus the glowdischarge lamp included in the leakage circuit during the chargingperiod is to be used as an indicator during the testing period.

When the button I6, I3 has been pressed suiciently long for thecondenser 6 to have reached its nal voltage, usually three to fourseconds, which is indicated by the glow discharge lamp glowing steadilywith a definite luminous intensity, said button is released and thebutton i9 pressed instead for 5 to 8 seconds, the glow discharge lampbeing then connected, in series with the series resistance t, betweenthe condenser 6 and the condenser `3S to be tested. If the insulation isgood a single short -glow is obtained in the glow discharge lamp' 'i onaccount of the tested condenser receiving a charging current which isrinterrupted when the voltage difference between the condensers 6 and 3ohas fallen to the value of the quenching voltage of the glow dischargelamp '1. The relative duration of the glow is dependent also upon thedimensions of the series resistance 8. If the insulation is less goodthe voltage oi the charged condenser 35 will gradually drop on ac- Whenthe voltage. of l count of leakage until the voltage difference betweenthe condenser 6 and the condenser 36 under test has again risen to thevalue of the ignition voltage of the glow discharge lamp when a renewedcharging through the' glow discharge lamp takes place with consequentglow. The more frequently the glow phenomena return the poorer isevidently the insulation. If a strong and prolonged glow is obtained thetested condenser 3S has a very poor insulation. If upon pressing of thebutton 23 the incandescent lamp 22 will burn a short-circuit is at hand.

If in testing a faultless condenser one desires to observe, the chargingglow repeatedly, the condenser 36 must be discharged between every timethe button I9 is pressed. This can be effected by pressing the button23, the condenser 36 then discharging through the incandescent lamp 22and the battery I3.

The invention is of course not limited to the shown embodiment but canbe modied in diierent ways. It is thus conceivable to include in theleakage circuit an individual glow discharge lamp or other dischargepath the quenching voltage of which considerably exceeds the ignitionvoltage of theglow discharge lamp used during the testing period as anindicator. In this case a final voltage on the condenser 6 is obtainedwhich is practically independent of fluctuations in the maximum voltagegenerated by the induction coil. Furthermore, it is not absolutelynecessary to provide a leakage circuit in parallel with the condenser 6but said circuit can also be left out. Finally there can, of course, beused in place of an induction coil every other arrangement forgenerating 'a pulsating alternating current having different positiveand negative maximum values.

I claim:-

1. An arrangement for testing electrical insulation, comprising incombination a battery, an interrupter,an induction coil having a primaryand secondary winding, said primary fed by said battery through saidinterrupter, a condenser, a spark gap having stationary electrodes, saidcondenser and said spark gap connected in series with said secondary, aVoltage limiting leakage circuit including a` glow discharge pathconnected in parallel with said condenser, a testing circuit including acurrent indicating means, means for including an object to be tested insaid testing circuit, and means for connecting said testing circuit withsaid condenser when charged to the desired voltage.

2. An arrangement for testing electrical insulation, comprising incombination a battery, an interrupter, an induction coil having aprimary and secondary winding, said primary ed by said battery throughsaid interrupter, a condenser, a spark gap having stationary electrodes,said condenser and said spark gap connected in series with saidsecondary, a leakage circuit, a test circuit comprising means orconnecting the object tol be tested, a gas iilled electrical dischargevessel, means for connecting said discharge vessel either with saidleakage circuit or with said test circuit, thereby connecting either ofsaid circuits in parallel with said condenser, said vessel acting asvoltage limiting element when included in said circuit and acting ascurrent indicating means when included in said test circuit.

3. An arrangement for testing electrical insulation, comprising incombination a battery, an interrupter, an induction coil having aprimary and secondary winding, said primary connected in series withsaid interrupter and said battery, a condenser, a spark gap havingstationary electrodes, said condenser and spark gap connected in serieswith said secondary, a normally open leakage circuit connected inparallel with said condenser, a normally open test circuit connected inparallel with said condenser, an electric glow discharge device, aswitching means for including said discharge device in said leakagecircuit, thereby closing said'circuit and acting therein as a Voltagelimiting element, another switching means for including said dischargedevice in` said test circuit, thereby closing said circuit and actingtherein as a current indicating means, and means connected with saidswitching means for simultaneously opening one and closing the otherswitching means, and vice versa.

4. A portable apparatus for testing electrical insulation, comprising incombination a battery, an interrupter, an induction coil having aprimary and secondary Winding, said primary connected in series withsaid interrupter and said battery, a condenser, a spark gap havingstationary electrodes and being capable of passing current in bothdirections, said condenser and said spark gap connected in series withsaid secondary, a voltage controlling circuit comprising an impedance,said circuit adapted to be connected in parallel with said condenser, atest circuit comprising means for connecting the object to be tested, agas lled electric discharge device, switching means for connecting saiddischarge device with said leakage circuit, thereby connecting saidleakage circuit with said condenser and said discharge device actingtherein as a voltage controlling element, another switching means forconnecting said discharge device with said test circuit, therebyconnecting said test circuit with said condenser and said dischargedevice acting as a current indicating means, an incandescent lamp andanother switching means for connecting said incandescent lamp in serieswith the battery and the object to be tested, lamp to indicate anelectrical short circuit, if present.

ERIK EINAR MRTENSSON.

